290 CLASS REPTILIA. 



plucked out, and they will open and shut their mouth 

 after the head has been separated from the body during 

 several hours. Redi and Boyle have seen serpents still 

 exhibit some signs of the preservation of this faculty after 

 having remained about four-and-twenty hours in vacuo. 

 The rattle-snake which Tyson had occasion to dissect so long 

 ago, appeared to live many days after the skin had been torn 

 and most part of the viscera removed. 



These facts induce us to believe that the ophidians derive 

 their sensibility less from the brain than the nerves. 



The head, though in many species very voluminous, is 

 formed only in small part by the cranium, which closely 

 embraces the encephalon. It lodges, morever, the organs of 

 the senses, and gives attachment to the muscles destined to 

 move both the jaws and itself on the spinal column. 



The cranium of the ophidians advances between the orbits, 

 as in the frogs. It presents two frontals almost square, and 

 one parietal ; the occipital presents an apophysis directed 

 backwards, and bearing a particulai- bone, which is mobile, 

 and articulates with the lower jaw, and with the arches which 

 form the upper. The sub-sphenoidal foss is a little sunk, 

 but it is not limited by the clinoid apophyses. 



Their brain weighs little more than the seven hundreth 

 or eight hundreth part of the rest of the body. Its two 

 hemispheres form together a mass more broad than long. 

 The optic lids, hollowed each by a ventricle, are almost 

 globular, and placed behind the hemispheres, which do not 

 cover them, and have twice their volume ; all the regions of 

 the brain are smooth and without circumvolutions. 



The cerebellum, very small and flatted, has the figure of 

 the segment of a circle. 



The olfactory nerve presents no sensible bulb, and pro- 

 ceeds from the anterior extremity of the hemisphere. The 

 origin of the other nerves exhibits no peculiarity. But all 



